Decades of research has used parent report vocabulary checklists – the CDI – to quantify and <> language development. A large body of research using this and other methods has revealed that girls tend to know more words than boys, that earlier-born children tend to know more words than later-born children, and that children from higher SES families tend to more words than children from lower-SES families. This last set of findings has received particular attention – as we’ve seen from the other presentations in this symposium, it has important real-world consequences for children’s lives. Grouped by SES, the quantity and quality of language input that children receive predicts their vocabulary size and other language skills, and vocabulary at only 25 months old predicts cognitive and linguistic abilities at 8 years old.
How do we go beyond a simple breakdown of vocabulary by demographic factor and beyond just a correlation between input and vocabulary? To ask more fine-grained questions, we need more data…
median productive vocabulary at 24 months in english
girls 368.7, boys 272.4 (1.4 times larger) [wordbank]
first 355.3, second 297.6 (1.2 times larger) [wordbank]
higher SES 441.5, lower 287.9 (1.5 times larger) [fernald2013]
lowest SES group less than a third of words of highest SES group